Compliant coatings research: A guide to the experimentalist

doi:10.1016/S0889-9746(87)90182-4

Journal of Fluids and Structures

Volume 1, Issue 1, January 1987, Pages 55-70

https://doi.org/10.1016/S0889-9746(87)90182-4 Get rights and content

The study of compliant coatings has been an area of keen interest for about 30 years. Among the potential useful applications for such coatings are drag reduction, sound absorption, vibration control and noise shielding. There are, however, several important issues with regard to the reliability of the available experimental data. In the present article, some of these issues will be addressed with the objective of guiding newcomers to the field. The effects of background turbulence in a wind or water tunnel, accurate drag measurements, compliant wall motion, noise reduction, and the geometry and properties of the coatings used in the experiments will be among the outstanding issues discussed. Attempts will be made to explain some of the seemingly contradictory results available in the open literature.

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Cited by (33)

Experimental Hydrodynamics for Flow Around Bodies
2021, Experimental Hydrodynamics for Flow Around Bodies
Drag reduction performance and mechanism of a thermally conductive elastic wall in internal flow
2017, Applied Thermal Engineering
Citation Excerpt :
The interaction between elastic walls and fluid constitutes a significant subject that has been studied in theoretical and experimental research [1–9] since Kramer [10] found that the flexible skin of dolphin caused transition delay and drag reduction.
Types of thermally conductive elastic walls with different thicknesses were prepared to study the drag reduction performance among elastic and rigid walls. Nano graphene was used as a conductive filler, and viscoelasticity silicon rubber was used as the matrix. To study the performance of the walls, internal flow equipment with a testing system was designed based on differential pressure measurement. According to the experimental results, the thermally conductive elastic wall exhibited the most optimal drag reduction effect. The maximum drag reduction rate of the elastic wall reached 8.54%. At a flow speed of 1.5 m/s, the thermally conductive elastic wall reached a maximum drag reduction rate 1.17% higher than that of the elastic wall under the same condition. The thermally conductive elastic wall had two mechanisms. First, the elasticity deformation increased the boundary layer thickness and decreased the velocity gradient, reducing the shear force. Second, the heat produced by the elastic deformation of the thermally conductive elastic wall was conducted at the boundary layer and decreased the viscosity, resulting in drag reduction. The thermally conductive elastic wall should delay the aging process and increase the service life of fluid machinery.
Transmission of a turbulent boundary layer wall pressure field through an elastomeric coating
2012, Ocean Engineering
Citation Excerpt :
The smaller wavelength (or higher wavenumber) wall pressure fluctuations are attenuated, typically decaying exponentially across the coating as shown in Fig. 1. A significant amount of research was focused on the use of compliant coatings for drag reduction during the 1970s and 1980s (Bushnell et al. (1977), Gad-el-Hak (1986, 1987), Voropayev and Babenko (1978), Kanarskiy and Teslo (1980); Semenov et al. (1985)). Hess (1990) found that soft, highly compliant coatings in water could lead to reductions in mean wall shear stress of approximately 5% at most.
The wall pressure fluctuations beneath a turbulent boundary layer introduce flow-induced noise and vibration which limits the performance of acoustic arrays. One method for mechanically filtering this energy is to separate the acoustic sensors from the fluid–solid interface with an elastomeric coating. Long wavelength acoustic energy is transmitted across the coating, and shorter wavelength energy from convected turbulence is attenuated. Experiments were conducted in an acoustically quiet water tunnel to measure the wall pressure fluctuations under 0.635 mm and 1.27 mm thick elastomeric coatings. Autospectra, magnitude and phase of the coherence, and convection velocities are presented for the range of Reynolds numbers 7540<Re_θ<16,100. The autospectra display an exponential decay which increases with increasing frequency and coating thickness. A modified model of that given by Blake (1984) is shown to accurately predict the attenuations in the autospectra. The cross-spectral model given by Corcos (1963) is shown to be valid for measurements of the wall pressure coherence beneath the coatings.
Compliant coatings for drag reduction
2002, Progress in Aerospace Sciences
Compliant coating research is one of those areas which experienced its fair share of triumphs and debacles. For over forty years, the subject has fascinated, frustrated and occasionally gratified scientists and engineers searching for methods to delay laminar-to-turbulence transition, to reduce skin-friction drag in turbulent wall-bounded flows, to quell vibrations, and to suppress flow-induced noise. In its simplest form, the technique is passive, relatively easy to apply to an existing vehicle or device, and perhaps not too expensive. Through the years, however, claims for substantial drag and noise reductions were made, only to be later refuted when the results were more critically examined. There are several important issues with regard to the reliability of available analytical, numerical and experimental results. In this article, some of these issues, particularly as they relate to the search for drag-reducing compliant coatings, will be addressed with the objective of elucidating the potential pitfalls to newcomers to the field. Problem formulation with proper boundary conditions, impossibility of obtaining first-principles analytical solutions when the wall-bounded flow is turbulent, and limitations of existing numerical simulations will be elaborated. The effects of background turbulence in a wind or water tunnel, accurate drag measurements, compliant wall motion, and the geometry and properties of the coating used will be among the outstanding experimental issues discussed. Attempts will be made to explain some of the seemingly contradictory results available in the open literature.
Temporal stability of flow through viscoelastic tubes
2002, Journal of Fluids and Structures
The stability of the Hagen–Poiseuille flow of a Newtonian fluid in an incompressible, viscoelastic tube contained within a rigid, hollow cylinder is determined using linear stability analysis. The stability of the system subjected to infinitesimal axisymmetric or non-axisymmetric disturbances is considered. The fluid and wall inertia terms are retained in their respective equations of motion. A novel numerical strategy is introduced to study the stability of the coupled fluid–structure system. The strategy alleviates the need for aninitial guess and thus ensures that all the unstable modes within a given closed region in the complex eigenvalue plane will be found. It is found that the system is unstable to both axisymmetric and non-axisymmetric disturbances. Moreover, depending on the values of the control parameters, the first unstable mode can be either an axisymmetric mode with the azimuthal wavenumber n=0 or a non-axisymmetric mode withn =1. For a given azimuthal wavenumber, it is found that there are no more than two unstable modes within the closed region considered here in the complex plane. For both the axisymmetric and non-axisymmetric instabilities, one mode is a solid-based, flow-induced surface instability, while the other one is a fluid-based instability that asymptotes to the least-damped rigid-wall mode as the thickness of the compliant wall tends to zero. All four modes are stabilized, to different degrees, by the solid viscosity.
Compliant coatings: the simpler alternative
1998, Experimental Thermal and Fluid Science
Boundary layer manipulation via reactive control strategies is now in vogue, and this topic dominated the meeting in which the present paper was delivered. Reactive flow control requires sensors, actuators and control algorithms. The payoffs are handsome but the difficulties involved are daunting. There are however much simpler alternatives to this kind of sophisticated flow alteration devices and the present article discusses one such alternative: passive compliant walls. The paper reviews the important developments in the field of compliant coatings that took place in the past 10 years. During this period progress in theoretical and computational methods somewhat outpaced that in experimental efforts. There is no doubt that complaint coatings can be rationally designed to delay transition and to suppress noise on marine vehicles as well as other practical hydrodynamic devices. Transition Reynolds numbers that exceed by an order of magnitude those on rigid-surface boundary layers can be readily achieved. Recent theoretical work indicates that transition to turbulence could be delayed indefinitely, at least in principle, provided that optimized multiple-panel compliant walls are used. There is renewed experimental evidence of favorable interactions of compliant coatings even for air flows and even for turbulent boundary layers, but more research is needed to confirm these latest results.

View all citing articles on Scopus

View full text

Compliant coatings research: A guide to the experimentalist

Journal of Sound and Vibration

Journal of Sound and Vibration

Journal of Sound and Vibration

Boundary layer stabilization by distributed damping

Journal of Aeronautical Sciences

Boundary layer stabilization by distributed damping

Journal of the American Society of Naval Engineers

The dolphin's secret

The New Scientist

The dolphin's secret

Journal of the American Society of Naval Engineers

Boundary layer stabilization by distributed damping

Journal of the American Society of Naval Engineers

Die Widerstandsverminderung Schneller Unterwasserkörper Mittels Kiinstlicher Delphinhaut

Jahrbuch 1969 der Deutschen Gesellschaft fir Luft- and Raumfahrt

Boundary layer control-drag reduction by compliant surfaces

David Taylor Model Basin, Bethesda, Maryland, Report No. 1668

Flow noise and drag measurements of vehicle with compliant coating

U.S. Naval Ordnance Test Station, China Lake, California, Report No. 8518

Water tunnel measurements of turbulent skin friction on six different compliant surfaces of one foot length

British Admiralty Research Laboratory Report ARL/G/N9

Water tunnel measurements of skin friction on a compliant coating

British Admiralty Research Laboratory Report ARL/N3/G/HY/9/7

The hydrodynamic stability of flow over Krämer-type compliant surfaces. Part 1. Tollmien—Schlichting instabilities

Journal of Fluid Mechanics

Fluid flow with flexible boundaries

Turbulent damping by flabby skins

Journal of Aircraft

Skin friction coefficients of compliant surfaces in turbulent flow

Journal of Spacecraft and Rockets

Turbulent boundary layer characteristics of compliant surfaces

Journal of Aircraft

Skin friction of compliant surfaces with foamed material substrate

Journal of Hydronautics

Compliant surface drag as a function of speed

Journal of Spacecraft

Compliant coating skin friction experiments

AIAA Paper No. 69-165

The theory of skin friction reduction by a compliant coating in a turbulent boundary layer

Turbulent skin friction on compliant surfaces

AIAA Paper No. 69-164

Experimental evaluation of compliant surfaces at low speeds

NASA TM X-3119

Reexamination of compliant wall experiments in air with water substrates

Journal of Spacecraft and Rockets

Experimental investigation of drag on a compliant surface

Effect of compliant wall motion on turbulent boundary layers

Physics of Fluids

Boundary layer interactions with compliant coatings: an overview

Applied Mechanics Reviews

Review of compliant coating research of M. O. Krämer

RPJ Associates, Palos Verdes Peninsula, California, Report TR-0955-001

Stability of laminar boundary layers on compliant boundaries: theory and experiment at NMI Ltd

Growth of instability waves over compliant coatings

Bulletin of the American Physical Society

Interaction of compliant surfaces with transitional and turbulent boundary layers

On the interaction of compliant coatings with boundary layer flows

Journal of Fluid Mechanics

The response of a two-layer compliant coating to a turbulent boundary layer

Bulletin of the American Physical Society

An optical technique for measuring the flow-induced motion of a compliant surface

The response of elastic and viscoelastic surfaces to a turbulent boundary layer

Journal of Applied Mechanics

On the growth of turbulent regions in laminar boundary layers

Journal of Fluid Mechanics

The water towing tank as an experimental facility

Experiments in Fluids

An experimental study of turbulent flows over compliant surfaces

Journal of Sound and Vibration

An experimental study of the hydrodynamic drag on compliant surfaces: fluid property effects

Proceedings Eighth International Congress on Acoustics

Hydrodynamic drag and surface deformations generated by liquid flows over flexible surfaces